The GaN-based semiconductor is a compound semiconductor represented by the chemical formula:AlaInbGa1−a−bN (0≦a≦1, 0≦b≦1, 0≦a+b≦1)which is also called a III group nitride semiconductor, a nitride-based semiconductor and the like. The GaN-based LED element having a light emitting element structure such as a pn junction structure, double heterostructure, and quantum well structure composed of the GaN-based semiconductor can generate green to near-ultraviolet light, and it has been put to practical use in applications such as a traffic light and a display device. While the GaN-based LED element has been increasingly studied and developed to be applied to illumination purpose at the present, a higher output power is said to be required for practical purpose.
FIG. 19 shows a structure example of a GaN-based LED element according to a conventional technique. As shown in a cross-sectional view in FIG. 19, a GaN-based LED element 10 has a substrate 11, and a semiconductor laminate 12 composed of a plurality of GaN-based semiconductor layers formed on the substrate. The semiconductor laminate 12 includes a p-type layer 12-3 arranged at the most distant position from the substrate 11, a light emitting layer 12-2 arranged between the p-type layer 12-3 and the substrate 11, and a n-type layer 12-1 arranged so as to sandwich the light emitting layer 12-2 with the p-type layer 12-3. A light-transmissive conductive oxide film 14 is formed on the p-type layer 12-3, and a positive pad electrode 15 is formed on the conductive oxide film 14. The conductive oxide film 14 is made of indium tin oxide (ITO), for example. In such a GaN-based LED element having a conductive oxide film as an electrode, light absorption by a pad electrode formed on the conductive oxide film is pointed out as a factor that hinders the increase in output power of the LED element, and as its remedy, it is proposed to make the pad electrode of a metal material with a high reflectance (patent document 1). In addition, a pad electrode is an electrode to which a material used for making connection with an external electrode, such as a bonding wire, conductive paste, and brazing filler metal (including solder and eutectic alloy), is bonded.    [patent document 1] JP-A-2005-317931    [patent document 2] JP-A-2001-210867